Cellular radio networks now proliferate much of the world. Constructing these networks requires the careful work of cellular network engineers. To construct a cellular network, one must consider many variables, not the least of which is the use and re-use of radio frequencies or channels. Cellular base stations make use of several radio channels, which are usually grouped and subdivided into sectors. For instance suppose that a cellular network has available to it 18 radio channels. Further suppose that the base station is expected to provide 360 degree radio coverage. Most cellular systems today transmit and receive in three sectors or directions. It follows then that each sector would have at least one antenna that is able to transmit and receive over a 120 degree arc to the horizon. At least one such antenna is directed to one sector of the coverage area and the antennas are arranged in a triangular pattern to affect full 360 degree coverage. Amongst these three antennas, the various radio channels are assigned so that each antenna has one or more distinct radio frequencies that won't interfere with the channels in use at the other two antennas. Thus a cellular base station typically incorporates three antenna systems, oriented 120 degrees apart, each with one or more unique radio frequencies or channels.
A cellular network then consists of many such cellular base stations. Cells which are adjacent to each other must be careful not to cause interference with each other. Interference is caused when antennas can receive or transmit radio frequencies that are used by other adjacent cells, causing radio interference. To avoid this overlap or duplication of frequencies by adjacent or nearby cells, radio network engineers use a variety of engineering practices, computer simulations and field testing. One technique used is known as frequency re-use planning, which in essence limits the number of frequencies used by any one base station to a subset of the total inventory of frequencies, thus assuring that adjacent cells always have frequencies available that aren't used by other adjacent cells. This practice limits the total number of frequencies, and thus the total radio bandwidth per cell, to some fraction of the available bandwidth. Strict adherence to such plans is often a part of the network design process, but imparts an added cost to the network because valuable radio channels aren't used when on many occasions they could be.
An ideal network always exists on paper, but never in practice. The first problem to be encountered is the location of the cell itself. While on a flat featureless plain, absent of cell placement restrictions, local zoning, and any of a myriad of legal and physical restrictions, a perfect location could be found for any cell location. Reality dictates that cells go where they can be put. This results in a less than uniform cellular placement. Thus, frequency re-use, transmitter power levels and antenna vertical tilt all become variables in the actual construction of the network on a cell by cell basis.
Once the cell is built, an engineering team must “drive test” the area to verify the cell coverage area. Once many cells are constructed, more drive testing must be done to evaluate the overall performance of the network and correct any un-desired interference.